Unseen Progenitors of Luminous High-z Quasars in the R_h=ct Universe

TL;DR

This paper compares supermassive black hole growth in two cosmological models, predicting observable differences in high-redshift quasar detections that can help determine which model better describes the universe.

Contribution

It advances the comparison of black hole growth predictions in LCDM and R_h=ct cosmologies by estimating observable quasar fluxes and detection rates at high redshift.

Findings

R_h=ct predicts almost no detectable quasars at z~7 with upcoming telescopes.

LCDM predicts significantly higher quasar detection rates at high redshift.

Future observations can discriminate between the two cosmological models based on quasar counts.

Abstract

Quasars at high redshift provide direct information on the mass growth of supermassive black holes and, in turn, yield important clues about how the Universe evolved since the first (Pop III) stars started forming. Yet even basic questions regarding the seeds of these objects and their growth mechanism remain unanswered. The anticipated launch of eROSITA and ATHENA is expected to facilitate observations of high-redshift quasars needed to resolve these issues. In this paper, we compare accretion-based supermassive black hole growth in the concordance LCDM model with that in the alternative Friedmann-Robertson Walker cosmology known as the R_h=ct universe. Previous work has shown that the timeline predicted by the latter can account for the origin and growth of the > 10^9 M_sol highest redshift quasars better than that of the standard model. Here, we significantly advance this comparison by determining the soft X-ray flux that would be observed for Eddington-limited accretion growth as a function of redshift in both cosmologies. Our results indicate that a clear difference emerges between the two in terms of the number of detectable quasars at redshift z > 6, raising the expectation that the next decade will provide the observational data needed to discriminate between these two models based on the number of detected high-redshift quasar progenitors. For example, while the upcoming ATHENA mission is expected to detect ~0.16 (i.e., essentially zero) quasars at z ~ 7 in R_h=ct, it should detect ~160 in LCDM---a quantitatively compelling difference.